Variable-pitch pick and place device

ABSTRACT

Improved variable-pitch pick and place devices may include one or more improvements such as a mechanical linkage such as pantograph linkage, the linkage itself linked to a plurality of device-gripping mechanisms arranged in a row so as to keep uniform, though variable, spacing between the device-gripping mechanisms, with the number of such mechanisms being increased relative to the number of parts in the linkage for reduced tolerance stack-up and improved positioning accuracy. The horizontal position of the linkage may be fixed at a position not at an end thereof, and desirably within the middle third or at the middle thereof. The linkage may be controlled at three points. These point may include a vertically flexible but horizontally fixed link to a supporting structure at the middle of the pantograph, a link at one end of the pantograph to one side of an endless loop of timing belt, and a link at the other end of the pantograph to the other side of the endless loop of timing belt. The links to the timing belt at the ends of the pantograph may be made via two end-most device-gripping mechanisms. The position of the timing belt may be controlled by a servomotor with a position encoder, the servomotor controlled by a controller such as a computer. The device-gripping mechanisms may include a vacuum tip grounded and supplied with vacuum by an electrically-conductive vacuum tube.

FIELD

[0001] This invention relates to fabrication and testing of integratedcircuit devices, and particularly to pick and place devices forassisting in processing and testing of integrated circuit devices.

BACKGROUND

[0002] Modem electronics devices, such as integrated circuits orsemiconductor “chips” are rapidly increasing in performance andfunctionality, and in production quantity, while simultaneouslydecreasing in size and unit cost. To increase the productivity anddecrease the cost of electronic devices, it is desirable to decrease thetime and cost of all operations in the production cycle.

[0003] Cost efficiency and productivity of processes performed onindividual chips, such as burn-in, various test processes, binning, andthe like, require precise, high-throughput handling of many chips.Traditionally, chips were transported in a container such as amagazine—a container typically designed to hold a row of chips placedend-to-end by sliding them one-by-one into one end of the container.Chips were removed from a magazine and separated from one another forprocessing, and replaced in a magazine after processing, by the force ofgravity.

[0004] Chip handling systems which utilize the force of gravity toseparate and transfer the electronic devices have at least two inherentdisadvantages.

[0005] First, since modem electronic devices have become smaller andlighter than before, an individual electronic device may not havesufficient weight to be efficiently separated from the others bygravity. This may cause jamming. If such jamming occurs, it is usuallynecessary to stop the operation of the system to clear the jam, thuscausing a serious loss of time and efficiency. Furthermore, the risk ofjamming is greatly increased due to the configuration of the new typesof electronic devices, such as chips with leads (pins) on all sides ofthe package, instead of two opposing sides as in the conventional dualin-line package (DIP).

[0006] Second, to minimize jamming, the outer surface of the electronicdevice must be made sufficiently smooth so as to not cause any frictionor unwanted engagement with other devices or the magazine. However, thisis also impractical since the plastic molded packages of the devicesoften have some burrs remaining from the production process and it isnot generally economically practical to completely eliminate such burrs.

[0007] More recently, trays holding arrays of chips have been used fortransport and handling of chips instead of magazines. The individualchips occupy individual cells within the array, and are removed from andreplaced in the tray by a “pick and place” device. A pick and placedevice typically employs multiple individual vacuum grippers, arrangedin a row, to pick up and to place a row or column of chips. The pitch orspacing between the cells in the array is typically fixed, although thepitch may vary between different tray types. Also, the chips may have tobe transported from one tray or other holder, such as a precisor,multi-track chip runway or the like, to another holder having adifferent pitch. This may occur as part of a processing, testing, orpackaging operation or the like.

[0008] Some pick and place devices with multiple grippers have gripperspositioned at a fixed pitch. The pitch of such devices may match therequired pitch of an associated machine or process, or of a tray forsuch machine or process. However, a fixed-pitch pick and place devicemay often not match the pitch, of a tray or other type of chip holder,with which it must be used. In particular, where a tray or other chipholder does not match the pitch of a precisor, a multi-track runway, orany other chip holder to which the chips must be transferred, afixed-pitch pick and place device will be mismatched to at least one ofthe chip holders. This results in the pick and place device having topick-up or set-down of a row of chips one at a time rather thansimultaneously.

[0009] Variable-pitch pick and place devices have been developed, suchas the device disclosed in U.S. Pat. No. 5,290,134, to provide thecapability of simultaneous pick-up and deposit even where the pitch ofone holder may differ from that of another holder. Nevertheless, a needexists for improved variable pitch pick and place devices.

SUMMARY

[0010] A variable-pitch pick and place device with increased positioningprecision and increased flexibility, with decreased complexity and costand maintenance requirements, and with provision for electronic and thuseasily-programmable pitch control is provided by the various aspects andembodiments of the present invention.

[0011] According to one embodiment, a variable-pitch pick and placedevice includes a plurality of device-gripping mechanisms supported in ahorizontal row, the horizontal positions of the mechanisms beingelectronically controlled so as to maintain uniform, though variable,spacing or pitch between the device-gripping mechanisms. The desiredpitch may be set via a look-up table stored in a controller such as acomputer. An operator may select a tray type, or a machine or processtype or the like, to trigger a look-up operation in the look-up table toobtain a value used to control the pitch. The computer may then use thevalue from the table to cause the adjustment of the pitch between thegrippers to match a desired pitch. A controller or computer may also beused to control the pitch regardless of whether information on thedesired pitch and/or the value used to control the grippers is obtainedfrom a look-up table, entered manually, or calculated, or obtained byother means.

[0012] According to another embodiment, a variable-pitch pick and placedevice has a mechanical linkage, such as a scissors or pantographlinkage, itself linked to a plurality of device-gripping mechanisms soas to maintain uniform, though variable, spacing or pitch between thedevice-gripping mechanisms. The links to the plurality ofdevice-gripping mechanisms are positioned so as to allow an increasednumber of device-gripping mechanisms to be positioned along thepantograph linkage relative to the number of links in the linkage. Thisyields improved positioning precision and decreased total number oflinkage parts in the device.

[0013] According to yet another embodiment, a variable-pitch pick andplace device has mechanical linkage such as a scissors or pantographlinkage, itself linked to a plurality of device-gripping mechanisms soas to keep uniform, though variable, spacing between the device-grippingmechanisms, and also linked to a supporting structure, the link betweenthe linkage and the supporting structure not being at an end of thelinkage, but desirably being within the middle third and most desirablyat the middle of the linkage.

[0014] According to another aspect of an embodiment, a variable-pitchpick and place device may have a mechanical linkage, itself linked to aplurality of device-gripping mechanisms so as to keep uniform, thoughvariable, spacing between the device-gripping mechanisms, and theposition of the linkage may be controlled through three links to thelinkage, one relatively near the middle compared to the other two, andtwo relatively near the ends, compared to the one.

[0015] According to another embodiment, in a device having a mechanicallinkage such as a scissors or pantograph linkage for keeping uniform,though variable, spacing between electronic device-gripping mechanisms,the extension and contraction of the linkage is controlled by a timingbelt or, if desired, a chain. The belt may be a continuous loop, theloop having two sides defined between a drive pulley or sprocket and anidler pulley. One end of the linkage may be attached to one side of thebelt, the other end to the other. The linkage may also be anchoredhorizontally at the center thereof, such that the linkage is controlledfrom three points, providing improved position control due to decreasedstack-up of mechanical tolerances. A servo or the like may be used tocontrol the motion of the drive pulley. An encoder on the shaft of theservo motor can allow precise electronic control of the pitch of theelectronic device gripping mechanisms. Such electronic control lendsitself to programmed or otherwise automated pitch changes. As an aspectof the embodiment, the pitch of the grippers may be controlled using aprogrammed computer.

[0016] According to another embodiment, movable portions ofdevice-gripping mechanisms are supplied with both vacuum and electricalground via a single structure, such as an electrically conductive vacuumtube, eliminating the need for separate grounding wires for every suchmovable portion.

[0017] The invention is directed to these and other new and nonobvoiusaspects, both individually and in combination, of improvedvariable-pitch pick and place apparatuses as disclosed herein. The aboveand other aspects, features, advantages, and benefits of the presentinvention will be apparent from the description bellow, which proceedswith reference to following figures:

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is perspective view of a pick and place device according toone embodiment of the present invention.

[0019]FIGS. 2 and 3 are perspective views of a gripper mechanism thatmay be employed in an embodiment of the present invention,

[0020]FIG. 2 with a movable portion retracted,

[0021]FIG. 3 with the movable portion extended.

[0022]FIGS. 4 and 5 are perspective views of certain components,including a scissors or pantograph linkage, useful in an embodiment ofthe present invention,

[0023]FIG. 4 with the pantograph linkage contracted,

[0024]FIG. 5 with the pantograph linkage extended.

[0025]FIG. 6 is an elevation view of certain components, including ascissors or pantograph and a controller, useful in an embodiment of thepresent invention.

[0026]FIG. 7 is a schematic plan view of an example application of anembodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0027] An example embodiment of a pick and place head 41 for a pick andplace device is shown in perspective in FIG. 1, including twelveindividual example gripper mechanisms, some of which are indicated byreference character 31. An example embodiment of a single grippermechanism 31 is shown in detail in the perspective view of FIG. 2 inretracted position, and in FIG. 3 in extended position.

[0028] The head 41 of FIG. 1 comprises a support structure in the formof a frame 2 on which are supported the illustrated twelve grippermechanisms 31, six on one side and six on the other side of the frame.Each gripper mechanism 31 includes a gripper in the form of a vacuum tip12 (FIG. 2). The vacuum tips 12 of the gripper mechanisms on each sideof the frame 2 extend toward the center of the frame such that thevacuum tips from both sides are aligned together in a single row.

[0029]FIGS. 4 and 5 show the six example gripper mechanisms on theback-most side of FIG. 1, but with the frame 2 and the six grippermechanisms from the front-most side of FIG. 1 omitted. FIG. 4 shows theback six gripper mechanisms in a retracted position, while FIG. 5 showsan extended position. As alternate embodiments, more or fewer grippermechanisms may be included and such mechanisms may assume a form otherthan shown in these figures. Also, more than one row of gripper elementsmay be provided.

[0030] As shown in FIGS. 1 and 2, in the example gripper mechanisms 31,each gripper mechanism includes anchor block 32 to which a verticalmotion or “z-” actuator is attached. One form of such an actuatorincludes an air cylinder 10 mounted by a bracket 35 (FIGS. 2, 3) to asub-plate 33 which is coupled to an anchor block 32 (FIG. 1). Aircylinder 10 includes a piston 37 with a piston extension 38. Air ports34 (FIGS. 2, 3) are in fluid communication with the cylinder 10 to allowdelivery of driving air for driving the cylinder 10 in both the upwardand downward directions in this embodiment. A fixed flow control valve36 sets the speed of the downward stroke of the cylinder 10, which aidsin preventing damage to electronic devices handled by the grippermechanisms 31. In another embodiment, valve 36 is adjustable. As analternative embodiment, the cylinder may also be driven only in onedirection, (e.g. downwardly), with a biasing mechanism being used toreturn the cylinder.

[0031] The vertical position of the piston 37 of the cylinder 10 istransmitted to a vertically movable portion 23 of the gripper mechanism31. The downward motion of the piston 37 is transmitted via the pistonextension 38 to portion 23. A limiting spring 21 serves to limit thedownward force applied to the movable portion 23, to aid in preventingdamage to electronic devices handled by the gripper mechanism. Themovable portion 23 is slidably supported on the sub-plate 33 by a linearbearing 13 for upward and downward movement as the piston is operated.

[0032] An example gripper in the form of a vacuum tip 12 (FIGS. 2, 3) ismounted on the vertically movable portion 23. The vacuum tip 12 is influid communication, through a passage in the movable portion 23, withthe interior of a hose fitting 22 mounted on movable portion 23.Accordingly, suction may be supplied to fitting 22 via a hose 60 (shownin FIG. 2 in dashed lines) to provide suction at vacuum tip 12. In thisexample embodiment, the hose 60, the hose fitting 22, the body of themovable portion 23, and the vacuum tip 12 are optionally and desirablyformed of electrically conductive material, with the hose connected (atthe end not shown but indicated schematically by ground 43) to agrounded structure (not shown), to protect the handled electronicdevices from electrical damage from electrostatic discharge, straycurrents, or the like. This feature eliminates the need for a groundingwire for each movable portion 23 of each gripper mechanism 31 separateor discrete from the hose 60 by providing both a vacuum and a groundingpath with a single element (the vacuum hose). The vacuum hose may be anysuitable available conductive tubing, such as anti-static conductivenylon or polyurethane, such as the polyurethane tubing available fromSMC Pneumatics, Inc., of Indianapolis, Ind. under the designation TAU.Related components, such as fitting 22 and other fittings, may be ofmetal or other suitable electrically conductive materials. The tip 12has a suction cup end formed of a flexible material, such as conductivepolyurethane, for example.

[0033] In the operation of an individual example gripper mechanism 31,air is supplied to the cylinder 10 to lower the movable portion 23 suchthat the gripper 12 approaches an electronic device to be gripped. Acommon hard stop such as in the form of a stop rail 14 is provided onthe frame 2 in the example embodiment of FIG. 1 for each set of sixgripper mechanisms, providing a reliable means for limiting the extendedposition of each movable portion 23 to match the extended positions ofthe other movable portions 23. A vacuum is supplied to the vacuumfitting 22 to cause the vacuum tip 12 to grip the electronic device. Airis then supplied to the cylinder 10 to retract the piston extension 38and raise the movable portion 23 with the device to be gripped held bythe vacuum tip 12. An individual stop 40 (FIGS. 2, 3) engages the lowerledge of sub-plate 33 and limits the upward travel of the movableportion 23. With the movable portion in the retracted position, the stoprail 14 (FIG. 1) also functions as a crash guard by extending below thelowest portion of the vacuum tip 12 in the retracted position. Opticalthrough-beam sensors, such as optical through-beam sensor 20 (FIG. 1),may be used to detect, by beam interruption, for example, whether all ofthe movable portions 23 are up, and/or whether any are down, thusproviding feedback on the operation of the movable portions 23.

[0034] The individual example gripper mechanisms may be operatedindividually when selective transfer of electronic devices is desired,by selectively supplying the desired air pressure and vacuum to theindividual gripper mechanisms. This allows the example embodimentvariable pitch pick and place head to perform sorting for testing,binning, and similar operations and to pick up a full load of devicesfrom trays that may have gaps in various rows, with, for example,devices picked up from more than one row of a tray in order to fullyload the grippers.

[0035] The individual example gripper mechanisms are supported formovement along the direction of the row of vacuum tips 12. In theillustrated example, the gripper mechanisms (FIGS. 1 and 4) aresupported slidably on a guide rail 9, via a guide block 42 attached toeach respective anchor block 32, with one rail 9 for each of the twosets of six gripper mechanisms. The guide block 42 and the guide rail 9together constitute a form of linear bearing 8, as best shown in FIGS. 4and 5. The guide rail is an elongated member having a longitudinal axis.

[0036] With reference to FIGS. 4, 5 and 6, even spacing or pitch betweenthe gripper mechanisms is preserved in this example by a linkagedesirably arranged in the form of a scissors mechanism or pantograph 44comprised of rigid beams (some being indicated as 45) linked together toform a series of parallelograms. The parallelograms thus formed aredesirably in a plane which may be horizontal or in some otherorientation, such as desirably in a vertical plane, as shown in FIGS. 4and 5. The pantograph 44 may then be disposed within a central slot 46in the center of the frame 2 of the example embodiment of FIG. 1,allowing the head 41 to be of a narrower width than with a horizontallydisposed pantograph. As shown in FIGS. 4 and 5, each beam within theinterior portions of the illustrated pantograph is pivotally linked toanother beam both at a crossover point, some being indicated at 17,located at the midpoint of each beam and at both upper and lower pivotpoints (such as indicted at 19 for some of the beams) located at theends of the beam. The beams at the ends of the pantograph are linkedsimilarly, but are shortened so as to extend only to the crossoverpoint, or in the case of outermost beams 15 and 16, to respective linkpoints 18 a, 18 b (FIGS. 4, 5). Alternative pitch control devices may ofcourse be employed for the gripper elements, such as other linkagemechanisms or a screw-driven positioning block for each grippermechanism, for example, but a pantograph linkage is generally desirablefor overall simplicity and reliability.

[0037] In the illustrated pantograph embodiment, the link points 18 c atwhich the gripper mechanisms are pivotally attached via pins to thepantograph 44 are located midway between the crossover point 17 and thelower of pivot points 19 on each beam. Link points 18 a, 18 b are atethe same elevation. This location for the link points 18 a, 18 b and 18c provides twelve of the link points with only five total parallelogramsin the pantograph 44 (recall that the front-most set of six grippermechanisms is not shown in FIGS. 4 and 5). This location for the linkpoints 18 a, 18 b and 18 c provides about twice as many link points forthe same number of pantograph beams as compared to the less desirableoption in which the link points for the gripper mechanisms are at themidpoints 17. The link positions at link points 18 c provides twogripper link locations for every parallelogram, plus two more linklocations at 18 a, 18 b in the respective last parallelograms, ascompared to one link location for every parallelogram, plus one more atthe last parallelogram. In other words, the number of completeparallelograms in the structure is one less than half the number ofgripper link locations, as compared to simply one less than the numberof link locations. As this embodiment is merely a desirable example,other link points may also be used, to achieve an equal or even greaterincrease in the number of link points per parallelogram. Increased linkpoints per parallelogram provide more accurate position control, sincefewer links mean that a lower total number of mechanical tolerancesinfluences the total positioning error. Less total parallelogram partsalso provides a lower cost, lower maintenance head.

[0038] The position of the pantograph 44 in the direction along the rowof vacuum tips 12 relative to the frame 2 is controlled in this exampleby a ball-bearing supported roller 7 (See FIG. 1), in this case attachedto uppermost pivot point 19 or a first point at the center of thepantograph 44. The roller 7 rolls vertically between two roller plates49 attached to the frame 2 of the example embodiment of FIG. 1. Theroller 7 thus serves to locate or fix the position of the first pointand thus of the pantograph 44, in the direction along the row of vacuumtips 12, by a link at a position at or near the middle of thepantograph. It is desirable (but not precluded) that this first point orhorizontal locating link not be at an extreme end of the pantograph 44but rather at this center location, or at least within the middle thirdof the length of the pantograph so that tolerance stack-up is furtherreduced compared to positioning a horizontal locating link at or near anend of a pantograph linkage. Positioning a horizontal locating link atthe midpoint also preserves the midpoint of the row of vacuum tips 12during adjustment of the pitch of the tips 12. The roller 7 restrainsthe first point of the linkage against movement a direction along thelongitudinal axis of the rail.

[0039]FIG. 6 is an elevation view of certain example components relatedto controlling the extension of the pantograph and the resulting spacingbetween adjacent ones of the vacuum tips 12, including the grippermechanisms 31, the guide rails 9 (only one visible), and the pantograph44 without the frame 2, but including a motor housing 3, a timing belt4, and an idler pulley 11. The timing belt 4 constitutes one form of aten side force transmitting member and extends in a loop around a drivepulley 52, past the gripper mechanisms 31, and around the idler pulley11. The belt 4 may be a continuous belt. Desirably the belt may be anopen ended loop for easier assembly and replacement. In this case, forexample, the two ends of the belt may meet in one of the outermostgripper mechanisms 5, 6 and are held in place, for example, by a clamp.Only the frontward half of this loop 4 is visible in FIG. 6. Tension onthe loop of the timing belt 4 is established by two springs 58, situatedin respective bores 64. The idle pulley block 56 slides on two pins 66that are mounted to the frame 2. After block 56 is positioned such thatthe springs appropriately tension the belt, the idle block is locked inposition, such as by set screws 68 which are tightened to clamp theblock to the pins.

[0040] In this example embodiment, the extension of the pantographlinkage is controlled by the positions of the outermost grippermechanisms 5 and 6, which in turn are controlled by the position of thetiming belt 11. The outermost gripper mechanism 5 is attached to thefront-facing side of the loop (visible in the figure) of the timing belt4, such as by a clamp 65 or other suitable means at a second locationpoint. The outermost gripper mechanism 6, at the opposite end of thepantograph 44, may be similarly attached to the rear-facing oppositeside of the loop (not visible in FIG. 6) of the timing belt 4 at a thirdpoint or location.

[0041] When the timing belt is rotated such that the front-facingsurface of the belt moves to the right in FIG. 6, as shown by the arrowA, gripper mechanism 5 is moved toward the right in the figure, whilegripper mechanism 6 is moved an equal distance to the left, thuscontracting the pantograph 44 and uniformly reducing the pitch of thevacuum tips 12. Motion of the timing belt in the opposite directionexpands the pantograph 44 and increases the pitch of the vacuum tips 12.Thus, the relative horizontal positioning and the expansion andcontraction of the pantograph linkage is controlled in this specificexample at three points: at the first point or location by the roller 7which rolls against the roller plates 37, and at the outermost grippermechanisms 5 and 6, rather than at only two points. That is, moving thetiming belt adjusts the spacing between the second and third pointsalong the longitudinal axis of the rails, resulting in an adjustment inthe length of the linkage and of the spacing between the grippermechanisms. Although not required, the use of three-point controlreduces positioning errors due to stack-up of mechanical tolerances.

[0042] The position and motion of the timing belt 4 is controlled by amotor such as a servo motor 46 positioned within a motor housing 3. Theservo motor 46 drives a drive shaft 50 through a gearbox 48. The drivepulley 52 that controls the motion of the timing belt 4 is mounted onthe driveshaft 50. The servo motor 46 also drives an encoder 54 fordetecting and controlling the position and motion of the servo motor 46and the driveshaft 50 and drive pulley 52.

[0043] A controller 60 may be employed to electronically control theposition of the servo motor 46. The controller may be in the form of adedicated chip or a portion of a chip or the like, or of a programmablecomputer or the like, or virtually anything in between. The controller,of whatever type, may include or be connected to a user interface 62.The controller may have a look-up table with values stored therein thatcorrespond to amounts of rotation or the positions of the shaft 50 thatcorrespond to desired pitch settings. The user may enter a desired traytype or a desired pitch measurement or the like to trigger a look-upoperation in the look-up table in the controller 60. The resulting valuemay then be used by the controller to determine and control the motionof the servomotor 46 so as to set the desired pitch. Alternatively, thecontroller may calculate the required motion or position of theservomotor 46 directly. The desired pitch information may be deliveredto the controller from any source. Limit switches 24 and 25 (FIG. 1) maybe used to detect the maximum and minimum extension of the pantograph bydetecting the presence of the gripper mechanism 5. One of the limitswitches 24, 25, may also serve as a home switch, to find a definedposition after power-up, in the event that the motor'sencoder/controller requires it.

[0044] Use of a non-slip tensile force-transmitting member such as thetiming belt 4 allows efficient, direct conversion of rotary to linearmotion and vice-versa, so that fine control of vacuum-tip pitch may beprovided via the rotary servo motor 46 and the rotary encoder 54. Thisallows easy electronic and programmable control of the pitch, based oncontrol of the servo motor 46. Furthermore, the pitch is always andimmediately adjustable to virtually any pitch within the total range ofadjustment, since the adjustment mechanism does not require nor rely onmechanical stops to define the pitches between which adjustment isdesired. Of course other tensile-force transmitting members may be used,such as chain or similar drive mechanisms. Although less desirable,other drive mechanisms, including those with stops, may be used.

[0045] The present invention, as illustrated in the various examplesabove, provides improved positioning precision and improved flexibilityin setting the pitch of a variable pitch pick and place device. Thepresent invention is useful in any context where relatively largenumbers of ICs need to be handled and/or sorted quickly and efficiently,particularly where a transfer between holders or containers of differentpitch is required. The pick and place device of the present inventionmay thus be used to move or selectively move ICs to and from all kindsof holders or containers, including trays, bum-in-boards, and machinecomponents such as precisors and multi-track IC runways. Devicestypically utilizing such transfers include many or even most back-endprocesses, including, for example, Bum-in Board Loaders and Unloaders,Trim-Form Machines, and Test Handlers.

[0046] An example application is illustrated in a schematic plan view inFIG. 7. A variable pitch pick and place head (VPH) 41 is supported on anx-z actuator 80 for controlled motion in the x- and z-directions. TwoVPHs (41, 41 a) may each be used at once in parallel for higherthroughput, with each VPH picking devices from respective sets of two ormore trays, such as trays 82, 84 and 82 a, 84 a. After a desired load ofdevices is picked by either VPH, the respective VPH, with the aid of therespective x-z actuator, moves the devices all at once to a respectiveprecisor 86, 86 a. Each precisor comprises a plate 88, 88 a withprecisely positioned cavities for holding the devices. The cavitiestypically have sloped sides so that gravity aligns the devices as theydrop into the cavities in the precisor plate. The respective load head90, 90 a then moves the devices all at once from the precisor to aburn-in board 92 for processing. The variable pitch of the VPH allows itto pick up all devices in a given tray row at once, and to set down allthe devices it can carry into the respective precisor all at once,regardless of any pitch mismatch, thus markedly improving loading speedover non-variable pitch designs.

[0047] Variations within the scope and spirit of the invention discussedabove will be apparent to those of skill in the art. For example: Notall of the gripper mechanisms need be movable with respect to the frame.One such gripper mechanism could, for example, be fixed relative to theframe, if desired, with the others being supportable by a pantograph orother structure so as to be movable along a first axis to establish adesired pitch between all of the grippers (including the fixed positiongripper). Thus, at least a plurality of the grippers in this case aresupported for this movement. Further, the number of vacuum tips or otherdevice grippers need not be twelve in number, but can easily be more orless than this. Moreover, the device need not include only a single rowof device grippers—multiple rows could be pitch-adjusted in parallel.Such variations are many and are not limited to these examples.Accordingly, the invention is defined not by the particular embodimentsand variations explicitly described herein, but by the claims below.

I claim:
 1. A method for moving electronic devices from a first locationto a second location using a plurality of electronic-device gripperswhich are spaced apart from each other along a row, the methodcomprising: picking up electronic devices with the electronic-devicegrippers at the first location and with the electronic-device grippersat a first pitch or spacing; selecting a desired pitch or spacing forthe electronic-device grippers; and electronically controlling theadjustment of the pitch between the electronic-device grippers from thefirst pitch to the desired pitch.
 2. The method of claim 1 furthercomprising moving the electronic-device grippers, and thereby theelectronic devices carried by the electronic-device grippers, from thefirst location to the second location, and releasing the electronicdevices from the electronic-device grippers at the second location. 3.The method of claim 1 further comprising picking up respectiveelectronic devices with the electronic-device grippers from a firstholder at the first location, adjusting the pitch between theelectronic-device grippers to the desired pitch, and placing theelectronic devices in a second holder at the second location.
 4. Amethod for moving electronic devices from a first location to a secondlocation with a plurality of electronic-device grippers arranged in arow and spaced apart from each other along the row, the methodcomprising: picking up respective electronic devices with theelectronic-device grippers at the first location and with theelectronic-device grippers at a first pitch or spacing; selecting avalue corresponding to a desired pitch or spacing for theelectronic-device grippers from a look up table; and adjusting the pitchbetween the electronic-device grippers to a desired pitch based upon thevalue obtained from the look up table.
 5. A method for moving electronicdevices, comprising: providing a plurality of electronic-device grippersarranged in a row and a frame supporting said plurality ofelectronic-device grippers for movement along the row; picking uprespective electronic devices with said plurality of electronic-devicegrippers; and adjusting the spacing between adjacent electronic-devicegrippers to adjust the spacing between adjacent electronic devices whilemaintaining the center of the row of electronic-device grippers at afixed position relative to the frame and maintaining equal spacingbetween adjacent electronic-device grippers.
 6. The method of claim 5wherein the act of picking up respective electronic devices with saidplurality of electronic-device grippers comprises moving at leastselected electronic-device gripper downwardly to a down position forpicking up a respective electronic device, detecting whether all of theselected electronic-device grippers are in the down position, andactivating each of the selected electronic-device gripper to grip arespective electronic device while in the down position.
 7. The methodof claim 6 comprising optically detecting whether all of the selectedelectronic-device grippers are in the down position.
 8. The method ofclaim 6 wherein all of the electronic-device grippers are moved togetherto the down position.
 9. A method for moving electronic devices with aplurality of gripper mechanisms, the method comprising: moving at leastone of the gripper mechanisms downward toward a down position forgripping a respective electronic device; detecting whether the at leastone of the gripper mechanisms is in the down position; activating the atleast one gripper mechanism to grip a respective electronic device;moving the at least one gripper mechanism upward toward an up position;and adjusting the spacing between gripper mechanisms.
 10. The method ofclaim 9 further comprising optically detecting whether all of thegripper mechanisms are in the down position.
 11. The method of claim 9further comprising detecting whether all of the gripper mechanisms arein the up position prior to adjusting the spacing between the grippermechanisms.
 12. The method of claim 9 comprising the act ofelectronically controlling the adjusting of the spacing.
 13. The methodof claim 12 further comprising detecting whether all of the grippermechanisms are in the up position prior to adjusting the spacing betweenthe gripper mechanisms.
 14. A method for moving electronic devicescomprising: providing a plurality of gripper mechanisms arranged in arow and carried by a pantograph linkage for movement along the row;picking up the electronic devices with a respective gripper mechanism;and applying a moving force to the pantograph linkage adjacent to oneend of the row in a first direction and applying a moving force to thepantograph linkage mechanism adjacent to the other end of the row in asecond direction opposite the first direction for varying the length ofthe pantograph linkage and thereby changing the spacing between thegripper mechanisms along the row.
 15. The method of claim 14 wherein themoving force is applied in the first direction to the outermost grippermechanism at the one end of the row to thereby apply the force in thefirst direction to the pantograph linkage through such gripper mechanismand wherein the moving force is applied in the second direction to theoutermost gripper mechanism at the other end of the row to thereby applythe force in the second direction to the pantograph linkage through suchgripper mechanism.
 16. The method of claim 15 further comprisingrotating a tensile-force transmitting member coupled to each of theoutermost gripping mechanisms to apply the moving force in the first andsecond directions to the outermost gripper mechanisms to vary the lengthof the pantograph linkage.
 17. A method for varying the spacing betweenelectronic devices carried by a plurality of gripper mechanisms arrangedin a row, the method comprising: applying a vacuum to the grippermechanisms to cause the gripper mechanisms to carry respectiveelectronic devices; electronically controlling the adjustment of thespacing between gripper mechanisms, to vary the spacing between theelectronic devices carried by the gripper mechanisms from a firstspacing to a second spacing.
 18. The method of claim 17 furthercomprising moving the gripper mechanisms, and thereby the electronicdevices carried by the gripper mechanisms, from a first location to asecond location, and releasing the vacuum on the gripper mechanisms toplace the electronic devices at the second location.
 19. The method ofclaim 17 wherein the gripper mechanisms are supported on a pantographlinkage and the method further comprises the act of maintaining a firstlocation of the pantograph linkage at a fixed position when the spacingbetween gripper mechanisms is adjusted to the second spacing.
 20. Themethod of claim 19 wherein the first location is in the middle third ofthe row.
 21. The method of claim 20 wherein the first location is at thecenter of the row.
 22. The method of claim 17 wherein the grippermechanisms are supported on a pantograph linkage and a tensile-forcemember is coupled to the outermost gripper mechanism at each end of therow, and the act of electronically adjusting the pitch between grippermechanisms comprises electronically controlling the movement of thetensile-force member from a first position to a second position to causea change in the length of the pantograph linkage and a correspondingchange in spacing between the gripper mechanisms to the desired spacing.23. A method of supporting electronic-device grippers so as to be ofvariable pitch or spacing, the method comprising: supporting a pluralityof electronic-device grippers on a pantograph having first and secondends at spaced apart locations; extending the pantograph in a firstdirection to increase the pitch between the electronic-device grippersand retracting the pantograph in a second direction opposite of thefirst direction to decrease the pitch between the electronic-devicegrippers; and restricting a first location of the pantograph frommovement in the first and second directions, the first location beingintermediate the first and second ends of the pantograph.
 24. The methodaccording to claim 23 wherein the first location is within the middlethird of the pantograph.
 25. The method according to claim 24 whereinthe first location is at the center of the pantograph.
 26. The methodaccording to claim 23 wherein the act of supporting comprises supportinga plurality of electronic-device grippers on a vertically orientedpantograph.
 27. The method according to claim 23 comprising the act ofapplying a force to respective second and third locations of thepantograph to extend and retract the pantograph, the second and thirdlocations being on opposite sides of the first location from one anotherand adjacent to the respective first and second ends of the pantograph.28. A method of extending and retracting a pantograph supporting aplurality of electronic-device grippers to vary the pitch or spacingbetween the electronic-device grippers, the method comprising: couplinga tensile force transmitting member to the pantograph at first andsecond spaced apart locations; driving the tensile force transmittingmember in a first direction to extend the pantograph and increase thespacing between the electronic-device grippers; driving the tensileforce transmitting member in a second direction opposite to the firstdirection to retract the pantograph and decrease the spacing between theelectronic-device grippers; and electronically and selectivelycontrolling the driving of the tensile force transmitting member. 29.The method according to claim 28 comprising the act of electronicallycontrolling a drive motor to control the driving of the tensile forcetransmitting member.
 30. The method according to claim 28 comprising theact of electronically controlling the driving of the tensile forcetransmitting member in response to values from a lookup table.
 31. Themethod according to claim 28 wherein the act of driving a tensile forcetransmitting member comprises driving a timing belt.